The Chinese premier, Wen Jiabao, called on disaster relief workers to step up their efforts today as the death toll from flooding in the south of the country rose to 199.

With more rain expected in the days ahead, the immediate danger was to communities below the collapsed Changkai dyke in Jiangxi province. Emergency rescue teams and troops were rushing to evacuate 12,000 people threatened by an upstream reservoir that was dangerously close to bursting its banks.

Nationwide, more than 2.4 million people have been forced from their homes by the torrential downpours, which have disrupted transport, damaged power supplies and ruined crops.

In Fujian and Guangdong, precipitation has been three times the annual average for this period in the rainy season, with up to 100cm (40in) of rain falling over the past few days.

Mudslides and raging torrents have been claiming close to 20 lives a day since the start of the rains on 13 June. With more than 123 people missing, the death toll is expected to climb.

"In the coming days another round of heavy rain will hit areas in the south. We are facing a bigger test, so we need to make better preparations to avoid disaster," Wen told the state-run CCTV channel. "We are in a crucial period. We must be fully prepared and step up organisation of disaster response work."

The annual flood has affected 25 million people in 10 provinces and caused economic losses estimated at 29.6bn yuan (£2.9bn), the civil affairs ministry said.

The water levels of at least 35 rivers, mostly in Fujian, Jiangxi and Hunan provinces, had exceeded warning marks and were threatening surrounding cities and farmlands, it said. The levels of six rivers were at record highs.

Soldiers and armed police have joined firefighters, police and hospital workers in assisting the victims and preventing greater damage, but their efforts have been hampered by damaged road and rail links.

Many residents have been evacuated by boat and helicopter. Extra supplies, including thousands of life vests and hundreds of rubber dinghies, have been rushed to the affected areas.

A total of 393,000 homes have been damaged, 144,000 have collapsed and nearly 1.36m hectares of crops have been affected, the government said.

Torrential rains were expected to continue for 10 days, according to the National Meteorological Centre.